em driver doesn't set multicast ethernet address

[iprebeg at freebsd.org]

While testing -CURRENT in VMWare environment, I discovered that em
driver doesn't properly set destination address in Ethernet header. In
the other words, when I start listening multicast session with mcastread
(mcast-tools), kernel triggers IGMPv3 packet. Its destionation IP is
224.0.0.22, but its destionation Ethernet address doesn't look like
01:00:5e:... Other machines that I run in same environment (like
FreeBSD-7) behave in good manner.